1. Field of the Invention
The present invention relates to a process of utilizing waste polymer material to manufacture useful products and more particularly to an improved process for making lubricating base oils from blends of waste plastics and Fischer-Tropsch waxes.
2. Description of Related Art
There is a steadily increasing demand for technology capable of converting discarded and waste plastic materials into useful products. This is due in large part to public concerns over potential environmental damage caused by the presence of these waste materials. According to a recent report from the EPA Office of Solid Waste, about 62% of all plastic packaging in the United States is composed of polyethylene, the preferred feed for plastics converted to lube oils. Plastics waste is the fastest growing waste product, with about 18 million tons per year in 1995 compared to only four million tons per year in 1970, and this amount is growing by approximately 10% per year. Transforming plastic waste material and particularly polyethylene into useful products presents a unique opportunity to address a growing environmental problem.
Because of environmental concerns, the specifications for fuels, lubricants and other petroleum products have become more stringent. This in turn has lead to a greater demand for lighter and cleaner petroleum feedstocks with the result that supplies of these feedstocks have been dwindling. In response to this, the production of synthetic lubricating oils from Fischer-Tropsch synthesized hydrocarbons has received increased attention, particularly in view of the relatively large amounts of natural gas reserves and the desire to convert these into more valuable products such as paraffinic lubricating oils. Accordingly, it would be advantageous to devise an economical process which converts waste plastic such as polyethylene into high viscosity index (VI) lube oils.
Processes are known which convert plastic waste into hydrocarbon oils. For example, U.S. Pat. No. 3,845,157 discloses cracking of waste or virgin polyolefins to form gaseous products such as ethylene/olefin copolymers which are further processed to produce synthetic hydrocarbon lubricants. U.S. Pat. No. 4,642,401 discloses the production of liquid hydrocarbons by heating pulverized polyolefin waste at temperatures of 150-500xc2x0 C. and pressures of 20-300 bars. U.S. Pat. No. 5,849,964 discloses a process in which waste plastic materials are depolymerized into a volatile phase and a liquid phase. The volatile phase is separated into a gaseous phase and a condensate. The liquid phase, the condensate and the gaseous phase are refined into liquid-fuel components using standard refining techniques. U.S. Pat. No. 6,143,940 teaches a process of converting waste plastics into high yields of heavy waxes. U.S. Pat. No. 6,150,577 discloses a process of converting waste plastics into lubricating oils. EP0620264 discloses a process for producing lubricating oils from waste or virgin polyolefins by thermally cracking the waste in a fluidized bed to form a waxy product, optionally using a hydrotreatment, then catalytically isomerizing and fractionating to recover a lubricating oil.
One drawback to any process which converts plastic waste into useful products is the fact that, as with any recycle feed, the quality and consistency of the starting material is an important factor in obtaining quality end products. Recycled waste plastic not only is quite variable in consistency but its quality varies from one extreme to the other due to the many grades and types of plastics on the market. Another key factor is the importance of having a constant and continuous supply to make the process economical particularly when using off-specification waste obtained from polyolefin processing plants (so-called xe2x80x9cvirginxe2x80x9d polyolefin). A process which economically and efficiently converts plastic waste into high VI lube oils while maintaining control over the quality and quantity of the waste plastic supply and insuring the quality of the end products would be highly desirable.
Therefore, an object of the present invention is to provide an economic and efficient process for converting plastic waste into high VI lube oils.
Another object of the invention is to improve the quality of waste plastic pyrolysis feeds and the quality of the end product.
Still another objective of the invention is to develop an improved process which pyrolyzes plastic waste in combination with Fischer-Tropsch waxy feeds to upgrade the quality of the resultant products.
These and other objects of the present invention will become apparent to the skilled artisan upon a review of the following description, the claims appended thereto and the Figures of the drawings.
The objectives and advantages of the present invention are attained by a process which comprises the steps of blending a wax derived from a Fischer-Tropsch process with a waste and/or virgin polyolefin, passing the combined stream to a heating unit which liquefies the blend and maintains it at a temperature below that at which any significant depolymerization or decomposition would occur, passing the liquefied blend to a pyrolysis reactor maintained at a temperature sufficient to effect depolymerization, passing the effluent from the pyrolysis reactor to a fractionator, recovering at least a heavy liquid fraction, passing the heavy liquid fraction to a catalytic isomerization dewaxing unit (IDW) and recovering a lubricating base oil. A preferred wax derived from a Fischer-Tropsch process for blending with the waste and/or virgin polyolefin includes a 1000xc2x0 F.+ Fischer-Tropsch wax fraction. If desired, the process can be conducted on a continuous basis.
Light fractions recovered from the pyrolysis effluent can be further processed and used as a feed for gasoline production. The light fraction can also be oligomerized to diesel and/or lube. Any middle fraction recovered also can be isomerization dewaxed and fractionated to recover diesel fuel, jet fuel and diesel blending stock. Alternatively, the middle fraction may be passed to a oligomerization reactor, followed by isomerization dewaxing and fractionation to recover high VI lubricating base oil. Any or all of the heavy liquid fraction, the light fraction and/or the middle fraction may be hydrotreated prior to the isomerization dewaxing step. The hydrotreating step is expected to remove nitrogen, oxygen and sulfur-containing contaminants, thereby, in certain cases, improving the effectiveness of the isomerization dewaxing process.
Preferably, the heavy liquid fraction obtained from fractionation of the pyrolysis effluent is blended with a heavy liquid fraction from a Fischer-Tropsch process, preferably including both a 1000xc2x0 F.xe2x88x92 fraction and/or a 1000xc2x0 F.+ fraction, the blend thereafter subjected to a catalytic isomerization dewaxing, and fractionated to recover a high VI lube oil and a bright stock (i.e. a lubricating oil hydrocarbon in which about 50 wt % boils over 1000xc2x0 F.).
In a separate embodiment, the feed to the pyrolysis reactor is a wax derived from a Fischer-Tropsch process. In this embodiment, a process for preparing a lubricating base oil comprises passing a wax derived from a Fischer-Tropsch process to a heating unit maintained at a temperature below the decomposition temperature of the wax; feeding the heated wax to a pyrolysis unit; pyrolyzing the wax to depolymerize at least a portion of the wax and recovering an effluent from the pyrolysis unit; processing the effluent in a separator to form at least a heavy liquid fraction; and, treating the heavy liquid fraction to produce a lubricating base oil.
Among other factors, the present invention is based upon the discovery that waste polyolefin can be economically and efficiently converted to high quality lubricating base oils by blending the waste with a Fischer-Tropsch heavy wax fraction, pyrolyzing the heated blend in a reactor, and subsequently hydrotreating and isomerization dewaxing a fraction obtained from the pyrolysis reactor. Using a Fischer-Tropsch fraction to supplement the polyolefin waste feed has eliminated the adverse impact on end-product quality caused by variations in the quality and consistency of the waste polyolefin used in the feed. When using virgin polyolefin as the waste polymer in the feed, the addition of a Fischer-Tropsch wax fraction obviates economical problems caused by variations in the cost and supply of polymer from industrial sites. Conducting the process on a continuous basis likewise contributes to economy and efficiency since smaller reactors can be employed and productivity increased.